Recent experience suggests that post-zygotic or mosaic mutations are a common cause of developmental disorders that can involve any organ system, although they are most easily recognized in vascular anomalies and skin. Several genes underlying rare syndromes with vascular anomalies have been identified, but so far only two that contribute to the more common non-syndromic forms: TEK for venous malformations and PIK3CA for lymphatic malformations, the latter recent work reported by the investigators. For both of these and several syndromic forms, the mutations are found in only or primarily in affected tissue and represent mosaic mutations. We propose to identify and study the genes underlying other vascular anomalies using new genomics technologies. The genetics community has rapidly moved to whole exome (WXS) or whole genome (WGS) sequencing to investigate disorders such as these, but the success rate of such studies is only ~25% when germline inheritance is expected, and much lower for patchy or asymmetric disorders that suggest mosaicism. Our first aim is to develop new genomic and bioinformatics methods that will more reliably detect low level mosaic mutations using massively parallel (NextGen) sequencing approaches. We will next study how the level and distribution of mosaicism affects the phenotype, focusing first on disorders with known causative genes (initially PIK3CA) that can be evaluated reliably because of vascular and/or lymphatic involvement. Finally, we will use existing and new methods to search for novel genes underlying vascular anomalies, focusing first on more common and clinically important types such as such as arteriovenous malformations, the remaining unexplained lymphatic malformations (that is, not due to PIK3CA mutations) and hemangiomas. We expect this work to significantly expand our understanding of vascular anomalies specifically and the nature of mosaicism more broadly.